This invention relates generally to advances in medical systems and procedures for prolonging and improving human life. More particularly, this invention relates to an improved system and method, including clusters or multiple coherent arrays of radiofrequency electrodes configured in an arrangement for producing large ablation volumes in tissue containing abnormalities such as cancerous tumors.
The use of radiofrequency electrodes for ablation of tissue in a patient""s body is known. In a typical situation, a radiofrequency electrode comprising an elongated, cylindrical shaft with a portion of its external surface insulated is inserted into the patient""s body. The electrode typically has an exposed conductive tip, which is used to contact body tissue in the region where the heat lesion or ablation is desired. The electrode is connected to a radiofrequency power source, which provides radiofrequency voltage to the electrode, which transmits the radiofrequency current into the tissue near its exposed conductive tip. This current usually returns to the power source through a reference electrode, which may comprise a large area conductive contact connected to an external portion of the patient""s body. This configuration has been described in articles, as for example, a research paper by Cosman, et al., entitled xe2x80x9cTheoretical Aspects of Radiofrequency Lesions in the Dorsal Root Entry Zone,xe2x80x9d Neurosurgery, December 1984, Vol. 15, No. 6, pp 945-950, and a research paper by Goldberg, et al. entitled xe2x80x9cTissue Ablation with Radiofrequency: Effective Probe Size, Gauge, Duration, and Temperature and Lesion Volumexe2x80x9d Acad Radio., 1995, Vol. 2, No. 5, pp 399-404. Radiofrequency lesion generators and electrode systems such as those described above are commercially available from Radionics, Inc., located in Burlington, Mass.
To enlarge ablation volumes, electrodes with curved conductive tips have been proposed. Such tips are injected from a cylindrical electrode placed near the targeted or desired tissue volume to produce an off-axis, curved arc within the targeted or desired tissue. In this way, off-axis ablation volumes may be produced away from the central axis of the inserted cannula. The off-axis lesions produced by these off-axis radiofrequency electrodes enlarge the lesion volume away from an axially symmetric, exposed electrode tip. One example of this type of an off-axis electrode is the Zervas Hypophysectomy Electrode available from the company Radionics, Inc., located in Burlington, Mass. Another example of this type of an off-axis electrode is the multiple side-emitting, off-axis electrode made by Radiotherapeutics, located in Mountainview, Calif. The multiple electrode elements range in curved arcs at various azimuthal angles. By making an umbrella of off-axis tip extensions at various azimuthal angles relative to a central insertion cannula, an enlarged lesion volume can be produced. Disadvantages of irregular heat ablation shapes and large central cannula sizes are discussed below.
Also, pairs of electrodes have been inserted into the body in a bipolar configuration, typically in parallel pairs held close to each other. Examples of such bipolar configurations are available from the company Elekta AB, located in Stockholm, Sweden. In such bipolar configurations, one electrode serves as a source and the other serves as a sink for the radiofrequency current from the RF generator. In other words, one electrode is disposed at the opposite voltage (pole) to the other so that current from the radiofrequency generator is drawn directly from one electrode to the other. The primary purpose of a bipolar electrode arrangement is to insure more localized and smaller heat ablation volumes. With such configurations, the ablation volume is restricted to the region between the bipolar electrodes.
Hyperthermia is a method of heating tissue, which contains a cancerous tumor, to thermally non-lethal levels, typically less than 45 degrees Centigrade combined with irradiation of the tissue with X-rays. Such application of mild non-lethal heating in combination with radiation by X-rays enhances destruction of cancer cells while sparing the normal cells from being killed. For hyperthermia, multiple arrays of high frequency electrodes are implanted in tumors. The electrodes are typically placed in a dispersed fashion throughout the tumor volume to cover the tumor volume with uniform heat, which is below the lethal 45 degree level. The electrodes are sequentially applied with high frequency voltage so that each electrode heats in sequence its neighborhood tissue and then. shuts off. Then, the next electrode does the same in a time series. This sequence of cycling the voltage through the electrodes continues at a prescribed frequency and for a time period ranging anywhere from minutes to hours. The primary objective of hyperthermia is not to fully ablate tumors by outright heat destruction of the cancerous tumor. On the contrary, its objective is to avoid temperatures above 45 degrees C. anywhere in the treatment volume. The article by Melvin A. Astrahan entitled xe2x80x9cA Localized Current Field Hyperthermia System for Use with 192-Iridium Interstitial Implants,xe2x80x9d in Medical Physics, 9(3), May/June 1982, describes the technique of radiofrequency hyperthermia.
Electrodes with cooled conductive tips have been proposed by Goldberg, et al., in their article referenced above. With cooling, electrode tips generally produce larger lesion volumes with radiofrequency electrodes, which are not cooled.
The electrode systems discussed above are limited by the practical size of lesion volumes they produce. For example, standard single cylindrical electrodes, with cool tips, as described above, make lesion volumes up to 3 to 4 cm in diameter in living tissue such as the liver using cannulae of 1 to 2 mm in diameter and several centimeters exposed tip length. The umbrella lesions made by multiple side-emerging, exposed tips, also produce lesion sizes of 3 to 4 cm volume diameter. A severe hazard of multiple extrusion of side-outlet electrodes is that it produces hemorrhaging by the multiple passes of the side outlet electrodes near the central cannula. Also, at the periphery of such side-emitting electrode lesions, irregularities and undulations in lesion shape and inhomogeneities in temperature around the side-emitted electrode tips produce hot and cold spots over the lesion volume. These may cause focal boiling and charring of tissue with unpredictable and dangerous consequences. For example, consider a large tumor of about 3 to 4 cm diameter in the liver. In such an example, there is a further risk that such undulations and variations in the shape of the periphery of the heat ablation zone would cause portions of the cancerous tumor to be missed by the heat ablation, which of course, would result in continued tumor growth and progression of cancer. Further, a single central cannula, which has one or many side-emitting radiofrequency electrode tips has a diameter, which increases with the number of radiofrequency tips that emerge from it. When the diameter reaches 3 to 4 mm for such a central cannula, there is the disadvantage of increased risk of hemorrhage and/or great pain or discomfort to the patient during insertion of the large central cannula into the tissue.
Thus, a configuration of radiofrequency electrodes, which can accomplish ablation volumes in the range of 4 to 6 cm diameter or greater for the purpose of adequately treating large cancerous tumors in the body are necessary to effectively destroy the tumor and combat cancerous cells from spreading. It is further necessary that such an electrode system involve a simple geometry, reduced numbers of tissue insertions, simple planning of needle placement, and simple planning of heat ablation geometry and distribution. An electrode system, which can be easily inserted into an organ or through the skin with minimal risk of hemorrhage and discomfort to the patient. An electrode system and method, which produces minimal lesion inhomogeneities to avoid complications of boiling and charring, and which avoids the inadvertent missing of outlying colonies of cancer cells in an irregular tumor is not only desirable, but necessary.
The present invention is directed to a system and procedure for using clusters or multiple arrays of electrodes arranged in a configuration for producing large ablation volumes in body tissue for effectively treating diseases such as cancer.
In one embodiment of the present invention, a parallel array of rigid, straight radiofrequency electrodes is inserted into body tissue that includes a cancerous tumor. The electrodes may be rigid metal tubes insulated over a portion of their length, except for their exposed conductive tips, which are shaped to terminate in pointed, tissue-piercing ends. The electrodes are configured in a cluster or array.
In one embodiment, the cluster is configured such that the electrode tips lie in close proximity to each other. Each electrode of the cluster is coupled to a radiofrequency generator located external to the patient""s body so that the conductive tips of each electrode in the cluster is raised to the same radiofrequency voltage. In this embodiment, the conductive electrode tips represent equipotential surfaces, which are positioned in proximity to each other. They create an effectively larger equipotential electrode due to the coherent voltage applied to all of them. This large effective electrode produces a larger ablation volume. Also, in some embodiments, by cooling fluid circulating within each of the electrodes in the cluster larger ablation volumes are formed. Lesion volumes of 4 to 6 cm diameter are easily accomplished, which is advantageous in many clinical situations, especially where curtailing large areas of cancer cells is necessary.
Contrary to existing electrode configurations and techniques, which propose inserting one large electrode into body tissue, thereby often causing severe hemorrhage, the present system of coherent cluster electrodes inserts into body tissue, multiple independent rigid electrode shafts of the cluster, each of appropriate small diameter, which reduces the risk of hemorrhage. The problem of irregular lesion ablation zones and inhomogeneities of ablation regions associated with prior side-emitting electrodes is also avoided by the coherent cluster electrodes of the present invention.
By applying the same radiofrequency voltage simultaneously to a cluster of electrodes accomplishes heat ablation effects vastly different from and far superior to heat ablation effects accomplished by applying the same voltage sequentially or serially to the same number of single electrodes (not in a cluster). With the coherent cluster electrode of the present invention, where the same or nearly the same radiofrequency voltage is applied to all the electrodes, the equipotential surfaces formed around the cluster are different from equipotential surfaces for individual electrodes of the cluster raised separately or sequentially to the desired RF potential. In some cases this may result in an heat ablation effect similar to that accomplished by using a single larger electrode. The present invention enables larger amounts of power to be deposited into the desired tissue area before hot spots occur around each electrode and raise the tissue temperature towards its boiling point. Furthermore, by cooling each of the electrodes, a larger withdrawal of radiofrequency heating power from the tissue proximate to the electrodes is accomplished when compared with cooling of only a single radiofrequency electrode within the cluster. Both coherent RF voltage application and cooled electrodes increase the lesion size associated with the cluster of RF electrodes.
Another advantage of the present invention is that by using the present cluster electrode system, the shape of the ablation volume may be controlled such that it is uniform at its outer margins. By way of one example, for a large cancerous tumor, which is irregular in shape, an ablation volume of sufficiently larger size may be formed to better ensure that the entire tumor is engulfed or consumed by the resulting heat lesion to destroy it completely. Planning where to place the coherent cluster electrode system is simpler than planning where multiple radiofrequency electrodes should be placed over an extended volume of tissue.
Yet another advantage of the coherent cluster electrode system of the present invention is that in accordance with one embodiment it enables all its electrodes to be inserted in unison and in a known geometric relationship to one another. In one embodiment, each electrode may be configured with a small shaft with a pointed, self-penetrating tip. Accordingly, the chance of a hemorrhage occurring from a multiple cluster of such smaller electrodes is less likely than with a single electrode of larger diameter. Even if the cluster of electrodes is not inserted in a precisely parallel fashion, the effect of their coherence in making a larger lesion volume is still effective.
The present coherent cluster of electrodes may configured in various ways, with or without cooling, to address specific clinical needs.